The present invention relates to a multiplex recording system and multiplex recording and playback system for VTR and, more particularly, to a system for recording an audio signal into and playing it back from a same track as a video signal.
As well known in the art, in a helical scan magnetic recording and playback apparatus (VTR), a plurality of rotary heads, such as two, are mounted on a drum or like rotatable member at an equal angular distance. A magnetic tape is wound around the rotary member over an angular range which may be a little over 180 degrees, for example. The rotary heads on the rotatable member are adapted to write video signals in the magnetic tape. Meanwhile, a stationary head is located in the path of travel of the magnetic tape so as to write audio signals therein. During playback, the rotary heads read the video signals and the stationary head, the audio signals.
A current trend in the art of video tape recording is to a longer record and playback time and, therefore, to a lower running speed of a magnetic tape. At the same time, there is an increasing demand for higher quality in the playback of audio signals. Because the relative speed between the running tape and the stationary head for writing and reading audio signals is low, there arises a dilemmatic situation that a decrease in the running speed of the tape significantly deteriorates the frequency characteristic of audio signals, compared to that of video signals which are written and read by the rotary heads, preventing audio signals from being reproduced with a desirable quality.
In light of this, there has been proposed a system which superposes an audio signal on a video signal after converting it into a predetermined mode, and records the superposed signals in a magnetic tape by means of a video signal read and write head and reads them out of the magnetic tape. In accordance with such a system, because a rotary head writes and reads an audio signal in and out of a magnetic tape which moves at a high speed relative to the head, the recording and playback quality is far higher than the system which writes and reads an audio signal by means of a stationary head without slowing down the movement of the tape.
In the proposed recording and playback system described above, an audio signal is subjected to at least frequency modulation and then superposed on a video signal which may be made up of a frequency modulated luminance signal and a low range carrier color signal, the superposed signals being written and read by a common rotary head. This brings about a problem that beat occurs between the carrier frequencies to develop interference (moire) in a reproduced picture.